Production of polyvalent metals



Sept. 6, 1960 s, DEAN 2,951,795

PRODUCTION OF POLYVALENT METALS Original Filed March 20, 1957 INVENTOR 0W A. 271W,

BY @va 15d ATTORNEYJ Patented Sept. 6, 1960 PRODUCTION OF POLYVALENTMETALS Reginald S. Dean, Hyattsville, Md., assignor to ChicagoDevelopment Corporation, River-dale, Md., a corporation of DelawareContinuation of application Ser. No. 647,206, Mar. 20, 1957. Thisapplication June 9, 1958, Ser. No. 740,865

6 Claims. (Cl. 204-64) This is a continuation of my application SerialNo. 647,206, filed March 20, 1957, now abandoned.

This invention relates to the production of pure polyvalent metals ofgroups IV-B, V-B and VI-B of the periodic system, in coarse crystallineform.

It is known that coarse crystals of these metals are produced by passinga direct current between two inert electrodes in a molten bathconsisting of alkalinous chlorides having dissolved therein chlorides ofthe polyvalent metal to be produced and also a significant amount ofalkalinous metal. It is necessary for the continued operation of suchbaths that a means of maintaining the content of polyvalent metalchloride be provided. For this purpose, comminuted or particulate metalis provided in the electrolyte around the inert anode providing what issometimes termed a disperse soluble anode. This comminuted materialdissolves to maintain the bath.

This manner of proceeding to make coarse crystals of titanium has beenfully described in a technical paper by the applicant entitled,Electrolytic Titanium, published by the Chicago Development Corporation,January 1957.

It has also been known to produce particulate titanium dispersed infused alkalinous chloride baths by sodium reduction and by passing adirect current through such baths, as for example, in British Patent No.678,807, dated May 11, 1951, to Shawingan Water and Power Company. Insuch procedures, it has been necessary to dissolve the salt bath fromthe particulate titanium dispersed in it before proceeding with furthertreatment of the metal. The dispersion of particulate metal in the salthas found no use per se. In fact, the eifort of most workers in thisfield has been to cause the particles to grow in size and thus break upthe dispersion.

In this invention, I make use of the dispersion as such and desire tohave it as permanent as possible. Since some settling may unavoidablytake place, I provide a stirrer in the cell and make provision to removeand recirculate any larger particles which may settle.

The replenishment of the electrolyte by a disperse anode is essentiallydifferent from normal electrorefining in which the direct electricalcontact is made with the material to be dissolved. To use a disperseanodej it is necessary to have an electrolyte in which the disperseparticles dissolve chemically but only to an equilibrium amount; thechange in electrolyte composition so brought about is then reversed bythe electrochemical action at the anode. In this way the electrolyte ismaintained.

The bobbin of the ordinary dry cell is a typical example of a disperseelectrode. MnO surrounding the real graphite cathode quickly saturatesthe Leclanch electrolyte with Mn ions but cathodic action reduces thedissolved Mn so that more Mn can be dissolved. In this way, MnO acts asan electrode material although not actually connected in the circuit.

I have so far illustrated the type of dispersion I use with dispersionsof titanium metal. Dispersions of the as chloride and from '.1-3%sodium.

polyvalent metals of group IV-B, V-B and VI-B may be produced byanalogous procedures. In addition, certain metallic compounds may beproduced dispersed in salt and these dispersions may be used to maintainthe bath. For example, the metallic compound ZrOl may be produceddispersed in a salt melt by the action of ZrCL, on Zr metal in a melt ofsodium chloride.

This invention, then, consists in'taking the particulate metal orelectrically conductive metallic compound in a salt bath, partiallyremoving the salt by settling of the metal, adding the dispersion soenriched in metal, either before or after solidification, to anelectrolytic cell in which the dispersion of metal or metallic compoundprovides the disperse soluble anode.

It will be clear that some of the salt bath must be.

removed with the crystals attached to the cathode so that the volume ofbath will be maintained by adding the particulate metal admixed withsalt. By suitable adjustment of current with respect to active anodesurface, the content of polyvalent metal chloride in the bath may bemaintained constant.

Having now described the general features of my invention, I willillustrate it by specific examples.

Example I In this example, I use as the source of the polyvalent metaltitanium dioxide. I reduce this oxide with carbon at 800 C. to increaseits ease of chlorination. I form this reduced titanium oxideapproximating 'Ti O in com-. position into pellets using an amount oftar so that on heating I obtain pellets containing the stoichiometricequivalent of oxygen and carbon to form oxides of carbon at 850 C. Iplace these pellets in a cell having a graphite anode in the midst ofsaid pellets; an electrolyte of fused sodium chloride is provided thecell. The cell with graphite-anode a and pellets b is shown in Figure 1.The cell is also provided with a steel cathode c as shown. When a directcurrent is passed through the cell, TiCl is formed in the anode zone andpasses through the molten electrolyte to the cathode zone whereparticulate Ti is formed and falls to the bottom of the cell where it isremoved through the gate d with about 25% of its weight as fused saltinto a second cell having an iron anode e and an iron cathode f and astirring device g to maintain the particulate titanium in suspension.The second cell is provided with an electrolyte of molten sodiumchloride in which is dissolved from 38% Ti When a direct current ispassed through the second cell, the particulate titanium is dissolvedand a salt layer with finely dispersed titanium crystals formed on thecathode, this is surmounted on further passage of the direct currentwith coarse crystal intergrowths of pure titanium frangibly attached bythe viscous salt layer to the cathode. From time to time the cathode islifted above the level of the electrolyte and into gas-tight drainingand cooling chamber h which surmounts and communicates with the secondcell, the chamber being closable by means of valve i and being operableat its top by means of closure member j, cooled out of contact with airand the crystal intergrowths removed and washed with dilute acid. Thepreformed cathode is returned to the bath which is replenished from timeto time by additions of particulate titanium and fused salt from thefirst cell. The washed crystals show less than .02% oxygen and no otherdeter:

of the second cell preferably is downwardly sloped, as,

shown at m, to provide a sump space n, from the lowermost part of whichlatter extends a draw-off conduit 0, provided with a draw-01f valve p,for the occasional withdrawal of bath material and settled out solidparticles.

Example II I In this'example, I use as the source of the polyvalentmetal chromite FeOCr O I mix powdered chromite with carbon in sufiicientamount to form CO from all oxygen present and form into pellets. Ichlorinate these pellets to form CrCl and FeCl which I condense assublimates. I add this sublimate'to molten sodium chloride alternatelywith small amounts of sodium to form a particulate metal having a ratioof chromium to iron of about 2l. This particulate metal settles in themolten NaCl and the enriched mixture of metal particles and salt iswithdrawn and is added to an electrolytic cell having an electrolyte ofNaCl having dissolved therein about 5% Cr, mostly as CrCl with a littleCrCl and about .1% sodium, an iron anode and an iron cathode. A directcurrent is passed through the cell causing the chromium to dissolve fromthe particulate metal and form chromium crystals attached to thecathode. The iron particles remain unattacked in the bath and from timeto'time the bath is withdrawn, cooled and pulverized and the ironremoved magnetically and the purified salt returned to the cell.

All of the operations described are carried out in the absence of air.

The chromium crystals are washed with dilute acid and on analysis'show99.9% chromium and less than 01% oxygen.

Example III In this example, I use Zirconium carbide as the source ofthe polyvalent metal and chlorinate it to produce ZrCl I add this to thecathode compartment of a diaphragm cell containing an electrolyte of 65SrCl 35 NaCl at 600 C. The ZrCL; is added at the rate at which it isreduced to metal by the alkalinous metal formed at an iron cathode. Agraphite anode is provided in the anode compartment and the chlorine isrecovered and used to chlorinate the zirconium carbide. Particulatezirconium is formed in the cathode compartment of the cell and settlesto the bottom from which it is recovered with about 20% of the fusedsalt bath. The mixture of bath and particulate zirconium is added to anelectrolytic cell having an iron cathode and anode, an electrolyte of65% SrCl 35% NaCl in which is dissolved zirconium as a mixture of ZrCland ZrCl having an average valence of 2.3 and 3% alkalinous metal. Thetemperature of electrolysis is 600 C. and zirconium crystals of highpurity are formed attached to the cathode. All of the operationsdescribed are carried out in an argon atmosphere.

The zirconium crystals are washed with dilute acid and analyze less than.01% oxygen and no determinable amounts of other impurities.

Example IV In this example, I take finely divided metallic zirconium inexcess and heat it in an inert atmosphere with fused sodium chloridecontaining ZrCl; under pressure at 825 C. After heating for 100 hours,the chlorine of the ZrCl has been converted entirely to ZrCl which isfound in dispersion in the salt as fine flaky particles. I feed thisdispersion continuously into a cell like that of g in the drawing andpass a direct current until the bath contains 10% suspended ZrCl throughthe bath at 200 amperes per sq. ft. on the cathode. Crystallinezirconium is formed on the cathode and the dispersion of ZrCl is thenfed at the rate necessary to maintain the zirconium content of the bath.The bath contains 3% zirconium dissolved as chloride, average valence2.1 and .5% dissolved metallic sodium.

I claim: 1

1. In a process for depositing a metal selected from a first groupconsisting of titanium, zirconium and chromium from an electrolyte of atleast one fused chloride of at least one second group metal selectedfrom the group consisting of alkali and alkaline earth metals anddissolved therein 2-10% of a chloride of the first group metal and .l3%of a metal selected'from said second group consisting of alkali metalsand alkaline earth metals by passing a current through said electrolytebetween two inert electrodes whereby to form a layer of finely dispersedcrystals of the metal of the first group in a salt layer on the cathode,the improvement which consists in continuing the passage of currentwhile replenishing the electrolyte with the metal to be deposited by theaddition to the electrolyte of a dispersion of particles of a materialselected from a group consisting of (a) the metal to be deposited and(b) an electrically conducting metallic compound of zirconium andchlorine, in a chloride of a metal of the second group, whereby toobtain the metal of the first group in the form of coarse crystalintergrowths adherent to the salt layer on the cathode.

2. In a process for depositing a metal selected from a first groupconsisting of titanium, zirconium and chromium from an electrolyte of atleast one fused chloride of at least one second group metal selectedfrom the group consisting of alkali and alkaline earth metals anddissolved therein 2-l0% of a chloride of the first group metal and .l3%of a metal selected from said second group consisting of alkali metalsand alkaline earth metals by passing a current through said electrolytebetween two inert electrodes whereby to form a layer of finely dispersedcrystals of the metal of the first group in a salt layer on the cathode,the improvement which consists in continuing the passage of currentwhile .replenishing the electrolyte with the metal to be deposited bythe addition to the electrolyte of a dispersion of particles of themetal to be deposited in a chloride of a metal of the second group,whereby to obtain the metal of the first group in the form of coarsecrystal intergrowths adherent to the salt layer on the cathode.

3. In a process of depositing zirconium from an electrolyte of at leastone fused chloride of at least one reducing metal of the groupconsisting of alkali and alkaline earth metals and dissolved therein2lO% of a chloride of zirconium and (LL-3.0% of at least one of saidreducing metals by passing a current through said electrolyte betweentwo inert electrodes whereby to form a layer of zirconium crystals in asalt layer on the cathode, the improvement which consists in continuingthe passage of current while replenishing the electrolyte with zirconiumby the addition to the electrolye of a dispersion of particles of ZrClin sodium chloride, whereby to obtain zirconium in the form of coarsecrystal intergrowths adherent to the salt layer on the cathode.

4. In a process of depositing zirconium from an electrolyte of atleast'one fused chloride of at least one reducing metal of the groupconsisting of alkali and alkaline earth metals and dissolved therein2-10% of a chloride of zirconium and 0.1-3.0% of at least one of saidreducing metals by passing a current through said electrolyte betweentwo inert electrodes whereby to form a layer of zirconium crystals in asalt layer on the cathode, the improvement which consists in continuingthe passage of current while replenishing the electrolyte with zirconium.by the addition to the electrolyte of a dispersion of particles ofzirconium metal in sodium chloride, whereby to obtain zirconium in theform of coarse crystal intergrowths adherent to the salt layer on thecathode.

5. In a process of depositing titanium from an electrolyte of at leastone fused chloride of at least one reducing metal of the groupconsisting of alkali and alkaline earth metals anddissolved therein2-10% of a chloride of titanium and OJ-3.0% of at least one of saidreducing metals by passing a current through said electrolyte betweentwo inert electrodes whereby to form a layer of titanium crystals in asalt layer on the cathode, the improvement which consists in continuingthe passage of current while replenishing the electrolyte with titaniumby the addition to the electrolyte of a dispersion of particles oftitanium metal in sodium chloride, whereby to obtain titanium in theform of coarse crystal intergrowths adherent to the salt layer on thecathode.

6. In a process of depositing chromium from an electrolyte of at leastone fused chloride of at least one reducing metal of the groupconsisting of alkali and alkaline earth metals and dissolved therein2-10%.of a chloride of chromium and (Ll-3. 0% of at least;v one of saidreducing metals by passing a current through said electrolyte betweentwo inert electrodes whereby to form a layer of chromium crystals in asalt layer on the 6 cathode, the improvement which consists incontinuing the passage of current While replenishing the electrolytewith chromium by the addition to the electrolyte of a dispersion ofparticles of chromium metal in sodium chloride, whereby to obtainchromium in the form of coarse crystal intergrowths adherent to the saltlayer on the cathode.

References Cited in the file of this patent UNITED STATES PATENTS2,734,856 Schultz et a1 Feb. 14, 1956 2,748,073 Mellgren May 29, 19562,760,930 Alpert et a1 Aug. 28, 1956 2,817,631 Gullett Dec. 24, 1957FOREIGN PATENTS 682,919 Great Britain Nov. 19, 1952

1. IN A PROCESS FOR DEPOSITING A METAL SELECTED FROM A FIRST GROUPCONSISTING OF TITANIUM, ZIRCONIUM AND CHROMIUM FROM AN ELECTROLYTE OF ATLEAST ONE FUSED CHLORIDE OF AT LEAST ONE SECOND GROUP METAL SELECTEDFROM THE GROUP CONSISTING OF ALKALI AND ALKALINE EARTH METALS ANDDISSOLVED THEREIN 2-10% OF A CHLORIDE OF THE FIRST GROUP METAL AND .1-3%OF A METAL SELECTED FROM SAID SECOND GROUP CONSISTING OF ALKALI METALSAND ALKALINE EARTH METALS BY PASSING A CURRENT THROUGH SAID ELECTROLYTEBETWEEN TWO INERT ELECTRODES WHEREBY TO FORM A LAYER OF FINELY DISPERSEDCRYSTALS OF THE METAL OF THE FIRST GROUP IN A SALT LAYER ON THE CATHODE,THE IMPROVEMENT WHICH CONSISTS IN CONTINUING THE PASSAGE OF CURRENTWHILE REPLENISHING THE ELECTROLYTE WITH THE METAL TO BE DEPOSITED BY THEADDITION TO THE ELECTROYLTE OF A DISPERSION OF PARTICLES OF A MATERIALSELECTED FROM A GROUP CONSISTING OF (A) THE METAL TO BE DEPOSITED AND(B) AN ELECTRICALLY CONDUCTING METALLIC COMPOUND OF ZIRCONIUM ANDCHLORINE, IN A CHLORIDE OF A METAL OF THE SECOND GROUP, WHEREBY TOOBTAIN THE METAL OF THE FIRST GROUP IN THE FORM OF COARSE CRYSTALINTERGROWTHS ADHERENT TO THE SALT LAYER ON THE CATHODE.